Both thermal and catalytic incineration is widely known and used for destruction of hazardous volatile organic compounds found in waste air and other gas streams which result from a variety of industrial processes. These streams result from processes for manufacture of organic chemicals and polymers, and from operations in which volatile organic solvents are used for cleaning and degreasing purposes in metal processing, machining and finishing. While catalytic incineration is able to operate at significantly lower temperatures and with considerably lower residence times than the thermal incineration alternative, additional equipment including a furnace and/or other heat exchange equipment have, typically, been required to provide a suitably elevated operating temperature to obtain catalytic activity for destruction of hazardous volatile organic compounds from a variety of industrial processes.
In any commercially viable application of catalytic incineration, special care is required in selection of an oxidation catalyst system appropriate to the volatile organic compounds which it is desired to destroy, and to avoid exposure of the selected catalyst to compounds which destroy its catalytic activity. Many of the gas streams which must be treated contain significant amounts of a halogen and/or halogenated compounds. However, precious metal catalysts used in conventional catalytic incineration are severely inhibited in their performance by the halogen atoms from the destruction of these compounds, and this desirable process cannot generally be used with such catalysts for these gas streams.
Recent and continuing interest in reduction of atmospheric pollution from internal combustion engines used in automotive and other vehicular applications is shown by numerous disclosures of apparatus for such intermittent operation. It is typically, stated that a reduction of atmospheric pollution and/or that some regulatory standard could be met using the disclosed apparatus. Achievement of significant improvement, however, may depend upon combination of any particular apparatus with modified engine designs and special fuels. Fuel quality improvements included, generally, both removal from the fuel composition of compounds which are known precursors of particular pollutants and blending with additional compounds which may change the composition of exhaust gases.
Recently issued U.S. Pat. No. 5,193,340 in the name of Tetsuya Kamihara and assigned to Nissan Motor Co. Ltd., is a representative of exhaust gas systems for internal combustion engine application. Most diesel engines are now equipped with a trap filter dispose in an exhaust passageway for trapping particulates and the like which are discharged from a diesel engine. When the back pressure of the engine increases due to the accumulation of the particulates trapped by the trap filter, the particulates are periodically burned to regenerate the trap filter. In the Kamihara apparatus the trap filter contains an oxidation catalyst for assisting burning of the particulates collected in the filter prior to regeneration. An injector valve is provided to inject diesel fuel into the exhaust passageway upstream of the trap filter, so that the trap filter is supplied with diesel fuel. The diesel fuel is burned in the trap filter under the action of the oxidation catalyst thereby burning the particulates so as to achieve a regeneration operation for the trap filter. When in operation, the amount of diesel fuel injected is controlled to increase as an intake air amount supplied to the engine increases and to decrease as an exhaust gas temperature increases, to limit or avoid thermal damage to the trap filter. When the particulates are periodically burned to regenerate the trap filter, the back pressure of the engine due to the accumulation of the particulates trapped by the trap filter is decreased thereby preventing the pack pressure from affecting engine performance. Undisclosed amounts of increased gaseous pollutants are exhausting to the atmosphere from the system during regeneration operation due to the additional diesel fuel burned.
Additional methods for filtering combustible particles from exhaust gases and rejuvenating the filter bed and its catalyst section are, for example, described in U.S. Pat. No. 4,322,287, U.S. Pat. No. 4,359,862 and U.S. Pat. No. 4,372,111 in the names of Kashmir S. Kirk and Martin Alperstein, and U.S. Pat. No. 4,359,863 in the names of Kashmir S. Kirk and Robert B. Burns, all assigned to Texaco Inc.
An earlier example of catalytic incineration equipment in which a gas-permeable bed of solids adapted to exchange heat with a gas stream is alternately heated with hot effluent from a catalytic oxidation bed and cooled with gas flowing into the bed by periodically reversing the direction of gas flow through the beds is described in U.S. Pat. No. 2,946,651 in the name of Eugene J. Houdry and assigned to Oxy-Catalyst, Inc. In operation, the patent states that sufficient diesel oil was injected into the heated gas stream and vaporized and then catalytically oxidized on the catalytic bed being used to heat the bed of gas-permeable solids. The catalyst employed was in the form of pellets of activated alumina impregnated with 5 percent of copper and chromium oxides and 0.1 inch in size. The heat exchange bed was the same size pellets composed of a dense fused alumina (Corhart).
Additional methods using preheating and or reversing flow for catalytic cleaning of exhaust gases are, for example, described in U.S. Pat. No. 4,059,676 in the names of Kang Yang and James D. Reedy, and assigned to Continental Oil Company; U.S. Pat. No. 4,877,592 in the names of Jury S. Matros, Viktor A. Chumachenko, Ljudmila J. Zudilina, Alexandr S. Noskov and Evgeny S. Bugdan, and assigned to Institut Kataliza Sibirskogo Otdelenia Akademii Nauk SSSR; Spetsialnoe Konstruktorsko-Technologicheskoe Bjuro Katalizatorov S Optnym Zavodim; and in U.S. Pat. No. 4,966,611 in the names of John C Schumacher, Joesph C. McMenamin, Lawrence B. Anderson, Harold R. Cowles and Stephen M. Lord, and assigned to Custom Engineered Materials Inc.
Regardless of the apparatus and methods employed, each commercial use depends, to be successful, upon selection of an oxidation catalyst appropriate to the volatile compounds which it is desired to destroy and the active lifetime of the catalyst in that system. Useful catalyst life is often limited due to exposure of oxidation catalysts to compounds which destroy their catalytic activity. Historically, the presence significant amounts of a halogen and/or organic and inorganic halogenated compounds in many of waste gas streams which must be treated has prevented the use of catalytic oxidation as a control technology for this application. It is believed the presence of halogen and/or compounds derived from halogen, whether or not such compound are destroyed in the process, deteriorate and temporarily poison the performance of precious metal catalyst.
Catalysts containing a noble metal (platinum), optionally in combination with other metals, for burning combustibles are described in U.S. Pat. No. 3,378,334 in the name of Herman S. Bioch and assigned to Universal Oil Products Company. Hydrated metal oxide catalysts have also been described. For example, U.S. Pat. No. 4,059,677 in the names of Edward J. Sare and Jerome M Lavanish, and assigned to PPG Industries, Inc., teaches that a waste containing C.sub.2 -C.sub.4 halogenated hydrocarbons, particularly unsaturated chlorinated hydrocarbons such as vinyl chloride, are incinerated in the presence of combination the hydrated oxides of manganese and cobalt. A supported catalyst system containing a Group VIII metal (platinum) is disclosed in U.S. Pat. No. 5,145,826 in the names of Eugene H. Hirschberg and George A. Huff, Jr., and assigned to Amoco Corporation. The disclosures of U.S. Pat. Nos. 3,378,334, 4,059,677 and 5,145,826 are specifically incorporated herein in their entirety by reference.
U.S. Pat. No. 5,292,704 in the name of George R. Lester and assigned to Allied-Signal Inc., teaches that a waste containing C.sub.1 halogenated compounds that do not have any carbon-hydrogen bonds are incinerated to carbon dioxide and halo acids (HCl, HBr, etc.) in the presence of specific combinations of a noble metal (platinum, palladium and rhodium), active catalytic components of titania, vanadium oxide, tungsten oxide, and optionally an effective amount of water. The disclosure of U.S. Pat. No. 5,292,704 is specifically incorporated herein in its entirety by reference. Halo acids are, however, very corrosive pollutants.
GB Patent No. 1,485,375 in the name of Goeffrey Colin Bond describes a process for degradation of a chlorinated hydrocarbon, in particular compounds containing more chlorine atoms than hydrogen atoms, by passing the chlorinated hydrocarbon into a bed of catalyst in which a fuel is "flamelessly" burning. In the Bond patent the term "degradation of a chlorinated hydrocarbon" is limited to formation of carbon dioxide and hydrogen chloride. The fact that exhaust gases from the degradation of a chlorinated hydrocarbon can also contain molecular chlorine is not mentioned. While scrubbing exhaust gases with water to remove the HCl is suggested in Bond, such scrubbing has not been found effective to remove all molecular halogens.
European Patent Application No. 0 485 787 A1 in the names of Masahiro Tajima and Masashi Harada describes treatment equipment of exhaust gas containing organic halogen compounds including a wash tower for removing hydrogen halide gas generated. Moreover, the patent states that in the case of decomposing the organic halogen compounds, the oxidative decomposition by oxygen most often generates halogen gas and the halogen gas generated is more difficult to remove than halogen halide. Without suggesting any direct method to remove halogen gas generated, the patent states that the existence of steam in the reaction gas may preferentially produce hydrogen halide.
It is therefore a general object of the present invention to provide improved apparatus and methods which overcome the aforesaid problems of prior art methods for abatement of carbon monoxide and volatile organic compound emissions from a from an industrial unit having a vent gas stream containing dioxygen, carbon monoxide, hydrocarbons and other organic compounds comprising one or more alkyl halide compound of 1 to 5 carbon atoms.
More particularly, it is an object of the present invention to provide integrated catalytic vent gas treatment systems for abatement of hazardous emissions from industrial processes using volatile chemicals.
It is another object of the present invention to provide integrated catalytic vent gas treatment systems that reduces air pollution by achieving reduced vent gas particulate levels emitted to the atmosphere.
It is another object of the present invention to provide integrated catalytic vent gas treatment systems that achieves reduced carbon monoxide and levels of potential pollutants at lower operating temperatures.
It is another object of the present invention to provide integrated catalytic vent gas treatment systems that achieves increased fuel efficiency and reduced fuel requirements while controlling carbon monoxide and levels of potential pollutants.
It is yet another object of the present invention to provide integrated catalytic vent gas treatment systems that extends incinerator equipment life, reduces maintenance costs, and reduces the frequency and duration of facility downtime.
It is yet another object of the present invention to provide integrated catalytic vent gas treatment systems with reduced energy costs.
While the above objects can be attained by integrated catalytic vent gas treatment systems according to this invention, other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims.